Hard disk drives are used in almost all computer system operations. In fact, most computing systems are not operational without some type of hard disk drive to store the most basic computing information such as the boot operation, the operating system, the applications, and the like. In general, the hard disk drive is a device which may or may not be removable, but without which the computing system will generally not operate.
The basic hard disk drive model includes a storage disk or hard disk that spins at a designed rotational speed. An actuator arm is utilized to reach out over the disk. The arm carries a head assembly that has a magnetic read/write transducer or head for reading/writing information to or from a location on the disk. The transducer is attached to a slider, such as an air-bearing slider, which is supported adjacent to the data surface of the disk by a cushion of air generated by the rotating disk. The transducer can also be attached to a contact-recording type slider. In either case, the slider is connected to the actuator arm by means of a suspension. The complete head assembly, e.g., the suspension and head, is called a head gimbal assembly (HGA).
In operation, the hard disk is rotated at a set speed via a spindle motor assembly having a central drive hub. Additionally, there are tracks evenly spaced at known intervals across the disk. When a request for a read of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head reads the information from the disk. In the same manner, when a request for a write of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head writes the information to the disk.
Over the years, the disk and the head have undergone great reductions in their size. Much of the refinement has been driven by consumer demand for smaller and more portable hard drives such as those used in personal digital assistants (PDAs), MP3 players, and the like. For example, the original hard disk drive had a disk diameter of 24 inches. Modern hard disk drives are much smaller and include disk diameters of less than 2.5 inches (micro drives are significantly smaller than that). Advances in magnetic recording are also primary reasons for the reduction in size.
However, this continual reduction in size has placed steadily increasing demands on quality control. For example, diligent inspection of hard disk drive components is essential to providing a high quality, reliable product.
One of the components in a hard disk drive which is important to inspect is the coil of wire used to form the conductor coil of the actuator arm that controls position of the read-write heads. Generally, the conductor coil is formed from a small diameter wire. The wire is generally made mostly of copper but also may be alloyed with other metals for improved strength. Normally, the wire is coated with an insulating sheath that is flexible enough to allow the wire to be shaped into a coil without undue damage to the insulation.
However, this insulation is subject to abrasion, cracking, pinholes or other degradation. The degradation can occur at any of the manufacturing stages of the wire including initial fabrication, coil winding, cleaning, up to and including final preparation and installation in the actuator arm. For example, during ultrasonic washing of the wire coil, erosion of the conductor itself can occur. In many cases, the erosion includes pinholes or other abrasions in the insulating coating. Failure to detect these defects prior to installation of the actuator arm in the hard disk drive can lead to hard disk drive failures.
Present methods exist for detecting insulated wire defects. However, as the insulated wire size is reduced, the present method is no longer able to detect the smallest abrasions or holes in the insulation. Moreover, the present testing method requires a testing sample that cannot rejoin the manufacturing process regardless of whether it passes or fails. For example, the present testing methods provide an organic solution on the insulation during the testing process. Because of the contamination of the organic matter with respect to the wire coils and the carriage assembly, after testing the test subject must be scrapped.
Thus, there is a need for a test method that is able to identify a small defect in the insulation while also permitting test components that are defect free to be returned to the manufacturing line and used in a functional hard disk drive.